This invention relates to a liquid crystal color display device, and more particularly to a liquid crystal color display device which includes locally different color display elements in one and the same device.
A liquid crystal color display device designed, for example, for automobile use, includes, for example, a bar-type display part for displaying the speed of an automobile in different colors. The bar is divided into, for example, four zones consisting of a green color zone, a yellow color zone, an orange color zone and a red color zone, and these color zones are progressively illuminated in the order of from the green color zone to the red color zone with an increase in the speed of the automobile.
As a means for exhibiting such locally different hues or exhibiting desired hues at desired portions only of a display pattern in one and the same display element in a liquid crystal color display device, a method is known in which a polarizing plate disposed on an upper side or a lower side of a twisted nematic type liquid crystal panel is locally colored in different colors, as disclosed in, for example, JP-A-No. 57-102611 laid open on June 25, 1982.
However, the method disclosed in the publication is defective in that, when it is desired to form a plurality of color display elements displaying colors other than the neutral color with one and the same polarizing plate means, the polarizing plate means must include polarizing plates dyed with the corresponding number of different dyes, and an increase in the cost is inevitable. In addition, the colored polarizing plate must then be bonded to the liquid crystal panel after the panel is formed. In this step, difficulty is encountered in accurately positioning the colored polarizing plate with respect to patterned display electrodes provided on the panel, and failure of accurate positioning leads to great degradation of the quality of display.
Also, a method as disclosed in, for example, JP-A-No. 57-172386 laid open on Oct. 23, 1982 is also widely known and used. According to the disclosed method, ink containing a pigment or a dye is printed as by screen printing on the surface of one of polarizing plates which is disposed nearer to a light source of a completed liquid crystal display device than the other. Three or four colors are usually printed in the same display device. In the disclosed method, black ink is printed on the area other than that occupied by the colored sections and display elements, in order to prevent misregister in printing and also to ensure a distinct display.
However, according to this method, the number of printing steps increases corresponding to the number of colors to be printed, and, when the black ink is used for the purpose of contouring, an extra printing step is additionally required. Also, since the colors are printed on the outer surface of the polarizing plate, the resistance to light is generally stressed as a matter of impartance, and, from this aspect, pigments instead of dyes are selected as coloring materials. However, the use of pigments lowers the transmittance of the ink and provides a display darker than when dyes are used. Further, there is the possibility of parallax between the ink films and the electrodes due to the spacing therebetween caused by the thickness of the substrate.